The present invention relates to catheters and more particularly to multiwall catheters made by a modified pultrusion process.
Current surgical techniques, such as in angiography, often require the use of a catheter which is inserted into a lumen of a vein or other blood vessel. Fluid is injected through the catheter, often at very high pressures, and serves as a contrast media for use in conjunction with diagnostic x-ray equipment.
Because these catheters are used inside a patient's body, they are subject to many strict, and yet conflicting requirements. For example, the catheter must be capable of negotiating a precise path within the patient's body, having the ability to change direction to enter any desired portion of the vascular system. Naturally, therefore, the catheter must be flexible enough to easily move through a blood vessel, and yet without undergoing permanent deformation. Also, the catheter must be stiff enough to be easily guided and controlled by a physician. The catheter physical characteristics are also subject to several strict, yet opposing requirements. For example, the outer diameter of the catheter must be kept small to fit through a minimum-size hole in an artery or vein, yet the inner diameter must be large enough to accommodate the desired fluid flow rates. In addition, the fluid flows frequently developed in angiography generate high pressures inside the catheter, and hence the catheter walls must be strong enough to resist bursting forces.
As even the smallest catheter will come into contact with the body, the catheter surface characteristics are also important. The catheter outer surface must be smooth and uniform to reduce friction and formation of blood clots (thrombosis). While various of the presently known catheters meet some of the above-mentioned conflicting requirements, no known catheter can boast of meeting all.
One approach to a blood clot resistant catheter surface has been to chemically bond an anticoagulant material to the catheter surface. The present invention offers a novel alternative to a chemically bonded anticoagulant.
One type of catheter which has proven effective is the multiwall catheter, formed by a plurality of co-extensive tubes. These catheters are generally manufactured by co-extruding two or more types of plastic tubes, frequently with a braid sheath of metal between the plastic tubes and serves to provide torsional rigidity while preserving longitudinal flexibility.
These known catheters have not been entirely successful because the metal braid is susceptible to kinking and permanent deformation. Such permanent deformation may result in catheter failure at the location of the kink. The wall thickness of several presently known extruded multiwall catheters has extra thickness to shield the stainless steel wire braid. Accordingly, contrast media flow has been compromised for a given catheter size.
Most presently known multiwall catheters are not inherently continuous, but instead have a tip portion welded to a body portion. In order that these known catheters may be guided by the physician and yet be capable of following a blood vessel, they are developed from a flexible distal tip welded to a more firm body portion. With such a construction there is always the possibility of the distal tip separating from the catheter thereby presenting serious problems.